This invention relates to optical fibres and, in particular, to the manufacture of optical fibres.
Optical fibres with a thin surface layer of silicon nitride or silicon oxynitride are known to show significant improvements in static fatigue performance as stress corrosion due to water attack is retarded. More recently, such surface layers have been found to be very effective barriers to the diffusion of free hydrogen into optical fibres. The thickness of the coating required is of the order of 200.ANG.. The methods of production of such known silicon nitride or silicon oxynitride layers on optical fibres involve chemical vapour base (CVD) techniques.